JPH07287471A - Fixing roller and fixing device - Google Patents

Abstract

PURPOSE:To provide a fixing roller and a fixing device capable of easily controlling a temperature, attaining a rapid temp. rise and also attaining energy saving. CONSTITUTION:The fixing roller 1 is constituted of a cylinder (cylindrical heating part) having a base part formed of a positive temp. coefficient thermistor, and a mold-released layer is formed on the outer peripheral part of the cylinder. And the fixing device is provided with the fixing roller 1, and also the device is provided with a magnetic circuit 3 being inter linked with the cylindrical heating part of the fixing roller 1, a primary coil 4 wound around the magnetic circuit 3 so as to be interlinked with the circuit 3 and a fixing energy supply part which is connected with the primary coil 4 so as to supply the power. By supplying the power to the primary coil 4 by the fixing energy supply part, making a current flow through the positive temp. coefficient thermistor of the fixing roller 1 as a secondary coil by electromagnetic induction so that the heating part may generate the heat by itself, the temperature necessary for fixation can be easily obtained and stabilized, then, the fixing device capable of easily controlling the temperature, attaining the rapid temp. rise and also attaining the energy saving can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing roller and a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer and a facsimile.

[0002]

2. Description of the Related Art In recent years, energy saving (hereinafter referred to as energy saving) of office automation equipment has become an increasingly important issue, and energy saving of a fixing device is no exception. As one point of energy saving in the fixing device, in order to reduce the energy consumption when the image forming device equipped with the fixing device is in the standby state, the temperature of the fixing roller is kept low to reduce the heat loss due to heat radiation. However, attention is focused on a method of rapidly rising to a predetermined fixing-enabling temperature when shifting from the standby state to the operating state.

Of course, such an idea has been around for a long time and has been put to practical use. However, to save energy more effectively, set the standby temperature lower than before, and more preferably leave it at room temperature without energizing it during standby to reduce heat loss during standby. It is desired to reduce However, if the temperature set lower than this is not rapidly raised to a temperature at which fixing is possible, the user of the image forming apparatus has to wait until the fixing roller reaches a predetermined temperature, which is an unnecessary point when using the apparatus. You will be forced to wait. That is, even if energy saving is achieved by such a method, it is not desirable from the viewpoint of ease of use of the device, and it is not an energy saving method widely accepted by users.

[0004] Against this background, various measures have been taken to accelerate the rise of the temperature of the fixing roller, because it is recognized that energy saving is achieved by increasing the rise of the temperature of the fixing roller. Usually, there is a limit to the electric power that can be applied to the fixing device, and there is a limit to increasing the applied power to speed up the start-up. Therefore, the heat capacity of the fixing roller is reduced so that the temperature rises faster even if the amount of heat given is the same. To reduce the heat capacity of the fixing roller, there is a method of reducing the thickness of the fixing roller or making the fixing roller from a material having a smaller specific heat.

Generally, when the heat capacity of the fixing roller becomes small, the temperature taken by the heat taken away when the fixing roller comes into contact with the toner or the transfer paper becomes large, and the heat necessary for the fixing cannot be supplied to the toner and the transfer paper. It cannot be fixed. Therefore, it goes without saying that there are restrictions in reducing the thickness of the fixing roller in terms of heat capacity and mechanical strength of the fixing roller. It is designed to be thin so that the temperature of the fixing roller rises quickly.

In addition, if the diameter of the fixing roller is reduced to reduce the heat capacity, the heating of the fixing roller is made efficient, and if the temperature required for fixing the fixing roller is lowered, the time required for start-up is shortened and energy saving is achieved. From the viewpoint of contributing, lowering the melting temperature of the toner has been performed.

[0007]

SUMMARY OF THE INVENTION The present invention solves the following problems, which become more prominent when the fixing roller is thinned and the temperature rises quickly, and reduces the heat radiation from the inner surface of the fixing roller. The task is to contribute to energy saving.

The first problem is that when the fixing roller rises quickly, the sensor itself detects the temperature of the surface of the fixing roller and the problem of heat transfer between the surface of the fixing roller and the sensor. A delay occurs, and a large overshoot occurs in the temperature of the fixing roller particularly when rising from normal temperature. The fact that there is a large overshoot also means that the temperature of the fixing roller has reached the temperature at which it can be fixed, but the sensor cannot detect that the temperature has reached the temperature, and therefore the rising speed cannot be utilized. The first object of the present invention is to solve this problem.

Further, in order to prevent the worst situation such as a fire from occurring when the fixing roller fails in a mode in which the temperature exceeds a set temperature and becomes higher and higher, it is necessary to install a temperature fuse or a thermostat. And so on. However, if the temperature rises quickly, due to a phenomenon similar to that described for the sensor in the first problem, the operation of the temperature fuse and the thermostat is delayed, and the temperature of the fixing roller when activated is much lower than that of a device with a slow rise. It becomes very hot, and the possibility of smoke, fire, etc. increases. The second object of the present invention is to solve this problem.

Further, if the thickness of the fixing roller is reduced in order to speed up the rise of the temperature of the fixing roller, the sectional area in the surface direction of the fixing roller becomes small, and it becomes difficult to conduct heat in the surface direction. That is, the thinner the fixing roller is, the smaller the cross-sectional area is, so that the heat conduction is significantly reduced. Therefore, when an image on a transfer sheet having a different width is fixed by an image forming apparatus including a fixing device including such a fixing roller, heat is taken away at a portion in contact with the transfer sheet,
Since heat is not taken away in the non-contact part, a temperature difference occurs between the part of the fixing roller in contact with the transfer paper and the part in non-contact.

For example, in the case of an apparatus capable of fixing the image of the transfer paper from the width in the longitudinal direction of A4 to the width in the lateral direction of the postcard with reference to the center of the length of the fixing roller, the image of the transfer paper having any width Since it is necessary to maintain the temperature of the contact part at a predetermined temperature even when fixing the paper, the sensor for controlling the temperature of the fixing roller uses the temperature of the part where the transfer paper of all widths is in common contact. It is installed at a position where it can be detected, and the temperature of the fixing roller is controlled based on the detected temperature. Therefore, when fixing an image on a transfer paper having a narrow width, heat is not taken from the fixing roller at a portion outside the width of the transfer paper, so that the temperature of the fixing roller at a portion not in contact with the transfer paper is higher than the temperature required for fixing. It gets expensive.

Further, if the heat conduction in the surface direction of the fixing roller is sufficiently performed, the heat of the high temperature portion moves to the portion where the heat is absorbed by the transfer paper, so that the temperature outside the width of the transfer paper does not rise. Although it is moderated, the fixing roller designed to be a thin fixing roller with a focus on quick start-up causes a remarkable temperature rise, and when the width of the transfer paper is changed from narrow to wide, the transfer Part of the paper comes into contact with the high temperature part and part of the paper comes into contact with the part with the preset temperature, causing wrinkles on the transfer paper, and exposing the toner to high temperatures causing part of it to decompose and smell. However, when the temperature exceeds the predetermined fixable temperature range, hot offset occurs and other inconveniences occur. In addition, the temperature of the portion not required for fixing becomes high, which is not preferable from the viewpoint of energy saving. The third problem of the present invention is to solve this problem.

In addition to the problems described above that become noticeable when the fixing roller is made thin and the temperature rises quickly, heat dissipation from the inner surface of the fixing roller, which has been difficult with the conventional heating of the fixing roller by a lamp, is difficult. It is another object of the present invention to contribute to energy saving by reducing the amount. As described above, the present invention can solve each of the above problems and also save energy.
An object of the present invention is to provide a fixing roller and a fixing device having a new structure.

[0014]

In order to achieve the above object, the fixing roller of the present invention comprises a cylinder whose base portion is formed by a positive temperature coefficient thermistor, and a release layer is formed on the outer peripheral portion of the cylinder. ing. Further, in order to reduce heat radiation from the inner surface of the fixing roller, a heat insulating layer is provided on the inner surface of the cylinder forming the base portion of the fixing roller. Further, a heat insulating layer and a reinforcing member are provided inside the cylinder in order to reduce heat radiation from the inner surface of the fixing roller and to reinforce the base portion.

To solve the above problems, the fixing device of the present invention is
A fixing layer is formed by forming a release layer on the outer peripheral surface of the base body made of a cylindrical positive temperature coefficient thermistor, and a magnetic circuit penetrating the inside of this fixing roller is provided, and the fixing roller is linked to this magnetic circuit. It is a one-turn secondary coil. Further, a coil wound so as to interlink with this magnetic circuit is provided as a primary coil. Then, a fixing energy supply unit that is connected to the primary coil to supply electric power is provided, and an AC voltage is applied to the primary coil to cause an electric current to flow in the positive temperature coefficient thermistor, which is a secondary coil, to generate heat, thereby generating the energy required for fixing. Supply.

Further, in the fixing device of the present invention, the temperature at which the resistance of the positive temperature coefficient thermistor suddenly changes is set higher than the temperature at which the cold offset of the toner to be fixed occurs and lower than the temperature at which the hot offset occurs. Further, means for detecting at least one of power, current, and voltage input to the primary coil is provided, and warm-up of the fixing device is determined based on the detection data.

Further, in the fixing device of the present invention, when the image forming apparatus equipped with the fixing device is in operation, the temperature characteristic of the resistance value of the positive temperature coefficient thermistor is maintained while the fixing energy supply unit is connected to the primary coil. Stabilizes the temperature of the cylindrical heating portion. Then, while the image forming apparatus is on standby, the temperature of the cylindrical heat generating portion of the fixing roller is changed to a predetermined temperature lower than the fixing temperature by limiting the electric power supplied from the fixing energy supply portion to a predetermined low value. Alternatively, the electric power supplied from the fixing energy supply unit is shut off while the image forming apparatus is on standby. Alternatively, while the image forming apparatus is on standby, the temperature of the cylindrical heating portion is stabilized to a predetermined temperature lower than the fixing temperature based on the output of the detector that detects the temperature of the fixing roller.

[0018]

In the fixing device of the present invention, a cylindrical positive temperature coefficient thermistor forming a fixing roller is used as a secondary coil, and a magnetic circuit penetrating the secondary coil and a primary coil wound around the magnetic circuit form a kind of transformer. Are configured. Therefore, when an AC voltage is applied to the primary coil, a current flows in the circumferential direction along the surface of the cylinder formed by the positive temperature coefficient thermistor which is the secondary coil. The positive temperature coefficient thermistor generates heat due to Joule heat due to this current. Due to this heat generation, the temperature rises and when it reaches a predetermined temperature determined by the characteristics of the positive temperature coefficient thermistor, the resistance value of the positive temperature coefficient thermistor suddenly changes and becomes high resistance. By designing the transformer so that only a very small current flows when the resistance becomes high, the amount of heat generated by the positive temperature coefficient thermistor is drastically reduced and the temperature rise of the fixing roller is stopped. When the temperature decreases due to heat transfer from the fixing roller to the surroundings, the resistance value of the positive temperature coefficient thermistor decreases and current flows to generate heat. Since this is repeated, in the fixing device of the present invention, the temperature of the fixing roller is maintained constant without performing special temperature control such as feedback control using a temperature sensor.

That is, in the fixing device of the present invention, the temperature of the fixing roller is stabilized to a predetermined temperature by the characteristic itself of the positive temperature coefficient thermistor which constitutes the fixing roller. However, even if the diameter is reduced or the input power is increased, the overshoot at the time of rising due to the delay in the response of the sensor as described as the first problem does not essentially occur, and this problem is solved.

As for the problem described as the second problem, the highest temperature portion of the fixing device is the fixing roller, and the temperature of the fixing roller is the material (positive temperature coefficient thermistor, etc.) constituting the fixing roller.
Since the temperature is maintained at a predetermined temperature due to the property, there is no possibility of causing thermal runaway, a temperature fuse, a thermostat, and other overheat prevention devices are not necessary, and the problem as pointed out does not occur essentially.

As for the problem described as the third problem, the fixing roller of the present invention is composed of a cylinder composed of a positive temperature coefficient thermistor, and since the current flows in the circumferential direction of the cylinder, the temperature is a predetermined temperature. If it reaches, the resistance of that part will become high, so no current will flow and energy will not be supplied, but in the low temperature part the resistance will be low, so current will flow,
Since energy is supplied to that portion, the temperature difference of the fixing roller does not occur due to the difference in the width of the transfer paper.

Further, in the fixing roller and the fixing device of the present invention, by disposing the heat insulating layer or the heat insulating layer and the reinforcing member on the inner surface of the cylinder forming the base portion of the fixing roller, the heat radiation amount from the inner surface side is reduced, It can contribute to energy saving.

[0023]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of the configuration of the main part of a fixing device according to the present invention. In the figure, reference numeral 1 is a fixing roller, 2 is a backup roller, 3 is a core, and 4 is a primary coil. The fixing roller 1 is a fixing roller in which a base portion is formed of a cylinder formed of a positive temperature characteristic thermistor, and a release layer is formed on the outer peripheral surface of the cylinder so that molten toner does not adhere when fixing. is there. A core 3 made of a magnetic material penetrates through the inside of the fixing roller 1, a primary coil 4 is wound around the core 3, and the core 3 as a whole constitutes a closed loop of a magnetic circuit. That is, a transformer is formed in which the fixing roller 1 is wound around the core 3 around which the primary coil 4 is wound as a one-turn secondary coil. When the primary coil 4 of this transformer is excited by alternating current, the core 3
A magnetic flux is generated in the fixing roller 1 as a secondary coil in response to a change in the magnetic flux. Therefore, an electric current flows in the circumferential direction through the cylindrical resistor formed by the positive temperature coefficient thermistor of the fixing roller to generate heat due to Joule heat, and the fixing roller is heated to raise the temperature.

FIG. 5 shows two types of typical temperature characteristics of the resistance value of the positive temperature coefficient thermistor, A and B. The temperature characteristics of the resistance value of the positive temperature coefficient thermistor are shown in FIG.
As in A and B, it is a peculiar one in that it rapidly changes at a specific temperature determined by the composition of the resistor. Therefore,
When the fixing roller is heated and its temperature rises and reaches a temperature at which the resistance value suddenly changes, the resistance value increases significantly. If the magnetic circuit of the transformer and the primary coil are set so that the current does not flow, the heat generation of the fixing roller is stopped. After that, if the fixing roller 1 is deprived of heat by the transfer paper or toner or radiates heat to the surroundings and cools, the resistance value decreases, so that current flows again to the fixing roller, heat is generated, and the temperature rises. Due to the characteristic that the resistance value of the positive temperature coefficient thermistor changes with temperature, the temperature of the fixing roller 1 becomes
It is stabilized at a predetermined temperature without a sensor for detecting the temperature of the fixing roller 1 or a device for feedback control based on a signal from the sensor.

The function of stabilizing the temperature by the characteristic of the positive temperature coefficient thermistor also works when fixing a transfer sheet having a width smaller than that of the transfer sheet which can be fixed by the fixing roller, and heat is applied to the transfer sheet. It not only stabilizes the temperature of the portion that is deprived, but also stabilizes the temperature of the portion that is not deprived of heat by the transfer paper. That is, unless the temperature of the part where heat is not taken down does not decrease, the resistance value of that part is high and current does not flow, so that the part is not heated. This is an electromagnetic induction method in which current is supplied to the fixing roller 1 in the circumferential direction to supply energy, so the current changes independently in the portion where heat consumption is small and in the portion where heat consumption is large in the axial direction of the fixing roller. This is because the entire roller is stabilized at a predetermined temperature. Therefore, in the fixing roller and the fixing device of the present invention, the problem of the edge temperature rise described in the section of the problem is essentially solved.

The backup roller 2 has a function of bringing the transfer paper into contact with the fixing roller 1 at a predetermined pressure, and the transfer paper is in a direction to bring the toner image into contact with the fixing roller 1 so that the fixing roller 1 and the backup roller 2 come into contact with each other. The toner image is fixed on the transfer paper by passing through the section.

FIG. 2 is a sectional view showing an embodiment of the structure of the fixing roller according to the present invention. The positive temperature coefficient thermistor 6 is a cylinder that forms the base portion of the fixing roller, and has a function of generating heat when a current flows through the cylinder and supplying energy required for fixing to the transfer paper and toner. A release layer 5 is formed on the outer peripheral surface of the cylinder formed of the positive temperature coefficient thermistor 6 so that the melted toner does not adhere at the time of fixing.

FIG. 3 is a cross-sectional view showing another embodiment of the structure of the fixing roller according to the present invention, in which a heat insulating layer 7 is added to the inner surface of the structure of FIG. The heat insulating layer 7 reduces heat dissipation from the inner surface of the fixing roller to save energy. Further, by reducing the heat radiation, the temperature of the fixing roller rises faster. Various materials can be used for the heat insulating layer 7 as long as they are materials that can be used at about 200 ° C. and have a heat insulating effect, but in this embodiment,
Good results have been obtained with glass cylinders or silicone rubber foam. In particular, when a glass cylinder is used, the mechanical strength of the glass cylinder can be utilized to play a role of reinforcing the cylinder of the positive temperature coefficient thermistor 6, so that the temperature of the fixing roller rises particularly quickly. This is particularly effective when the thickness is reduced in order to reduce the heat capacity of the positive temperature coefficient thermistor 6 with an emphasis on design.

FIG. 4 is a sectional view showing still another embodiment of the structure of the fixing roller according to the present invention, in which the heat insulating layer 7 and the reinforcing member 8 are added to the inner surface of the structure of FIG. The roles of the heat insulating layer 7 and the reinforcing member 8 are the same as in the embodiment of FIG.
There are various materials such as metal, glass and ceramics as the material of the reinforcing member 8. In this embodiment, a metal cylinder is used as the reinforcing member 8. However, since the metal is a conductor, the core of FIG. At least one slit (not shown) extending from one end to the other end is provided in the axial direction of the metal cylinder so as not to form a coil interlinking with the magnetic circuit formed by 3. Further, protrusions (not shown) extruded from the inner surface of the metal cylinder toward the surface are formed at predetermined intervals, and the protrusions support the positive temperature coefficient thermistor 6 to reinforce. An air layer is formed in the portion without the protrusion, and this is the heat insulating layer 7. Of course, a heat insulating layer having the same material and structure as those in the embodiment of FIG. 3 may be provided. When the reinforcing member 8 is made of metal, heat conduction is large and much heat is radiated in the portion in contact with the heat generating portion, but the positive temperature coefficient thermistor 6 has a constant temperature because the resistance value changes at a predetermined temperature. Since there is a characteristic that is maintained, the resistance of the part that radiates a lot of heat becomes lower than that of its surroundings, current concentrates and heat generation increases,
No temperature non-uniformity occurs.

FIG. 6 is a diagram showing an embodiment of the configuration of the control unit of the fixing device of the present invention, in which the fixing roller (secondary coil and resistor) 1, core 3, and primary coil of the fixing device shown in FIG. 1 are used. The transformer part consisting of 4 is displayed on the electric circuit,
4 is a circuit diagram showing a configuration of a fixing energy supply unit connected to the primary coil 4. FIG. In FIG. 6, a power source 9 supplies necessary power to a fixing device or an image forming apparatus including the fixing device. The power switch 10 has a function of controlling connection of the power supply 9. The converter 11 is configured by a primary coil 14, a secondary coil 15, and a core 17, which converts the commercial frequency power received from the power source 9 into direct current, converts the direct current power into alternating current with a frequency higher than the commercial frequency. It is supplied to the primary coil 14 of the transformer 12. The frequency of the power to be supplied ranges from several KHz to several 100 in order to make the device compact
Set to KHz. Since the cross-sectional area of the core 17 of the transformer 12 is inversely proportional to the frequency used, a thinner core can be used as the frequency becomes higher, which saves material and also makes the fixing roller, which is the secondary coil, thinner, so that the heat capacity is also increased. It is possible to lower the temperature of the fixing roller, and it is also effective to accelerate the temperature rise of the fixing roller.

The converter 11 performs frequency conversion and keeps the voltage of the primary coil 14 of the transformer 12 applied, but the resistance value of the resistor 16 becomes high at a predetermined temperature and it becomes difficult for current to flow. Since the electric power is reduced and the heat generation is reduced, the fixing roller 13 is maintained at a predetermined temperature. That is, the positive temperature coefficient thermistor that constitutes the fixing roller functions as the secondary coil 15 and the resistor 16, and the temperature of the fixing roller is determined by the resistance change characteristic of the positive temperature coefficient thermistor depending on the temperature. Therefore, in the present invention, the resistance value suddenly changes. The positive temperature coefficient thermistor has a characteristic that the temperature is between the temperature at which hot offset occurs, which is the upper limit when toner is normally fixed, and the temperature at which cold offset occurs, which is the lower limit temperature.

The converter 11 includes a primary coil 1
4 is provided with a detection device for detecting the current flowing through
With this detection device, the current after the power switch 10 is turned on is monitored, it is determined that the current has changed from a large state to a small state, and the control unit of the image forming apparatus including the fixing device is connected via the communication path 18 to The rising signal of the temperature of the fixing device is sent. It also has a function of stopping or starting the operation of the converter 11 in response to a command from the control unit of the image forming apparatus via the communication path 18. This function is used when the paper jam of the image forming apparatus occurs or is cleared. Moreover, not only the current is monitored, but also the voltage is monitored to make the detection of the rising edge more reliable,
The rise can also be detected by monitoring the power based on the voltage and the current and the phase difference between them.

The primary coil 14 and the secondary coil 1 shown in FIG.
5, a core 17 is the primary coil 4, the fixing roller 1, and the core 3 shown in FIG. Then, the fixing roller 1 is electrically finely disassembled and displayed, and is the fixing roller 13 including the secondary coil 15 and the resistor 16 in the figure. Further, the resistance 16 is an equivalent resistance for one round in the circumferential direction of the roller composed of the positive temperature coefficient thermistor.

Next, an embodiment corresponding to claim 7 will be described with reference to FIG. When a signal indicating a standby state is received from the control unit of the image forming apparatus via the communication path 18 described above, the energy supplied from the converter 11 to the primary coil 14 is limited to a predetermined value, or a duty for energizing the current is supplied. Is limited to a predetermined value, and the fixing roller 13 is held at a temperature lower than the temperature determined by the characteristics of the positive temperature coefficient thermistor. Such a function is used to reduce power consumption during standby and to reach a temperature at which fixing can be performed in a very short time from the standby state.

Next, an embodiment corresponding to claim 8 will be described with reference to FIG. When a signal indicating that the standby state is set is received from the control unit of the image forming apparatus via the communication path 18 described above, the function of the converter 11 is stopped and the power supply to the primary coil 14 is stopped. This is used to reduce the heat consumption of the fixing device during standby to the utmost limit. Usually, it is desirable to reduce the heat capacity of the fixing roller 13 as well, because the image forming apparatus becomes difficult to use unless the waiting time when resuming the use is shortened.

Next, an embodiment corresponding to claim 9 will be described with reference to FIG. The components denoted by the same reference numerals as those in FIG. 6 have the same functions, and the description thereof will be omitted. Normally, the temperature of the fixing roller 13 is stabilized by the temperature characteristic of the resistance of the positive temperature coefficient thermistor, and when a signal indicating a standby state is received from the control unit of the image forming apparatus via the communication path 18, the fixing roller 13 is received. Temperature controller 20 based on a signal from a temperature detector 19 provided to detect the temperature of the surface of the
Performs feedback control to a predetermined temperature lower than when the converter 11 is controlled to fix the fixing roller 13. Although this method is similar in operation to the embodiment corresponding to claim 7, in the embodiment corresponding to claim 7, the ambient temperature,
The temperature of the fixing roller during standby changes due to the influence of wind and the like, and the time from the standby state until the temperature reaches the fixable temperature changes accordingly. However, since the temperature detector 19 is used in this embodiment, The temperature of the fixing roller is maintained at a constant temperature without being affected by the ambient temperature and the like, and the time required to reach the fixable temperature from the standby state can be kept within a predetermined narrow range.

[0037]

As described above, according to the first aspect of the invention, since the positive temperature coefficient thermistor is used for the base portion of the fixing roller, the end temperature rise, the detection delay of the temperature detector, and the temperature overshoot. It is possible to configure a fixing device that solves problems such as an operation delay of the rising prevention device. Further, since the positive temperature coefficient thermistor, which has been difficult to attach an electrode in the related art, is formed into a cylindrical shape to allow electromagnetic induction heating, it is possible to solve the problem of supplying electric power for heating.

According to the invention described in claims 2 and 3, claim 1
In addition to the above effect, it is possible to reduce heat dissipation from the inner surface of the fixing roller, which contributes to energy saving and quick rise of the temperature of the fixing roller.

In the invention described in claim 4, the problems 1, 2, and 3 to be solved by the present invention can be solved. Further, since it is not necessary to detect the temperature of the surface of the fixing roller, the release layer on the surface of the fixing roller is not damaged by friction with the detector, and the life of the fixing roller can be extended.

In the fifth aspect of the invention, since the base portion of the fixing roller is a positive temperature coefficient thermistor, the temperature at which the temperature characteristic of the resistance changes changes to the temperature of the fixing roller as it is, so that the toner can be fixed. Good fixing can be achieved by selecting a positive temperature coefficient thermistor whose resistance changes in a wide temperature range. In the past, the heat generated by the thermistor was first transferred to a metal plate and then used, so the temperature at which the thermistor resistance changes due to the temperature gradient between them must be selected to be higher than the temperature to be used. In addition, the temperature gradient changes depending on the heat dissipation condition on the side that uses heat, and the temperature on the side that uses it varies widely, making it difficult to achieve a predetermined temperature.A positive temperature coefficient thermistor with appropriate characteristics should be used. Although difficult to select, in the present invention, since the base portion of the fixing roller is formed by the cylindrical positive temperature coefficient thermistor, these problems can be solved.

According to a sixth aspect of the present invention, means for detecting at least one of electric power, current and voltage input to the primary coil is provided, and warm-up of the fixing device is determined based on the detected data. Therefore, the rise of the temperature of the fixing device which does not use the temperature detector can be detected easily and without delay.

According to the seventh aspect of the invention, while the image forming apparatus is on standby, the temperature of the cylindrical heat generating portion is set to be lower than the fixing temperature by limiting the electric power supplied from the fixing energy supplying portion to a predetermined low value. To change to a lower predetermined temperature,
It is possible to control to a temperature lower than the fixing temperature during standby without a temperature detector.

According to the eighth aspect of the present invention, by stopping the function of the converter during standby, the heating of the fixing roller can be stopped, and significant energy saving can be achieved.

The invention described in claim 9 is another means for keeping the fixing roller at a low temperature in the standby state, and by providing a temperature detector for detecting only the temperature in the standby state, the fixing possible temperature is changed from the standby state. It becomes easy to set the time to reach the predetermined range. Since this detector only aims to detect the standby temperature, it can be set outside the range through which the image to be fixed passes. By doing this, the detector and the fixing roller can be set. The life of the fixing roller will not be shortened due to scratches caused by the contact of.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a configuration of a main part of a fixing device according to the present invention.

FIG. 2 is a sectional view showing an embodiment of the structure of a fixing roller according to the present invention.

FIG. 3 is a sectional view showing another embodiment of the structure of the fixing roller according to the present invention.

FIG. 4 is a sectional view showing still another embodiment of the structure of the fixing roller according to the present invention.

FIG. 5 is a diagram showing an example of characteristics of a positive temperature coefficient thermistor used for the base portion of the fixing roller of the present invention.

FIG. 6 is a circuit diagram showing an example of a configuration of a control unit of the fixing device according to the present invention.

FIG. 7 is a circuit diagram showing another embodiment of the configuration of the control unit of the fixing device according to the present invention.

[Explanation of symbols]

 1: Fixing roller 2: Backup roller 3: Core (magnetic circuit) 4: Primary coil 5: Release layer 6: Positive temperature coefficient thermistor 7: Thermal insulation layer 8: Reinforcing member 9: Power supply 10: Power switch 11: Converter 12: Transformer 13: Fixing roller 14: Primary coil 15: Secondary coil 16: Resistor 17: Core 18: Communication path 19: Temperature detector 20: Temperature control device

Claims (9)

[Claims] 1. A fixing roller of a fixing device equipped in an electrophotographic image forming apparatus, wherein a base portion is a cylinder formed of a positive temperature coefficient thermistor, and a release layer is provided on an outer peripheral portion of the cylinder. A fixing roller characterized by being formed. 2. A fixing roller of a fixing device equipped in an electrophotographic image forming apparatus, wherein a base portion is a cylinder formed of a positive temperature coefficient thermistor, and a release layer is provided on an outer peripheral portion of the cylinder. A fixing roller, characterized in that a heat insulating layer is formed inside the cylinder. 3. A fixing roller of a fixing device equipped in an electrophotographic image forming apparatus, wherein a base portion is a cylinder formed of a positive temperature coefficient thermistor, and a release layer is provided on an outer peripheral portion of the cylinder. A fixing roller, which is formed and provided with a heat insulating layer and a member for reinforcing the cylinder inside the cylinder. 4. A fixing device equipped in an electrophotographic image forming apparatus, comprising a cylindrical heating portion formed of a positive temperature coefficient thermistor and a release layer formed on the outer periphery of the cylindrical heating portion. A fixing roller, a magnetic circuit interlinking with the cylindrical heat generating portion, a primary coil wound so as to interlink with the magnetic circuit, and a fixing energy supply for supplying power by being connected to the primary coil. A fixing device having a section. 5. The fixing device according to claim 4, wherein the temperature at which the resistance of the positive temperature coefficient thermistor suddenly changes is higher than the temperature at which the cold offset of the fixing toner occurs and lower than the temperature at which the hot offset occurs. Fixing device. 6. The fixing device according to claim 4, further comprising means for detecting at least one of electric power, current and voltage input to the primary coil, and warming-up of the fixing device based on the detected data. A fixing device characterized by determining. 7. The fixing device according to claim 4, 5 or 6, wherein when the image forming apparatus including the fixing device is in operation, the resistance of the positive temperature coefficient thermistor is maintained while the fixing energy supply unit is connected to the primary coil. The temperature of the cylindrical heat generating portion is stabilized by the temperature characteristic of the value, and by limiting the electric power supplied from the fixing energy supply portion to a predetermined low value while the image forming apparatus is in standby, A fixing device characterized in that the temperature is changed to a predetermined temperature lower than the fixing temperature. 8. The fixing device according to claim 4, 5 or 6, wherein when the image forming apparatus including the fixing device is in operation, the resistance of the positive temperature coefficient thermistor is maintained while the fixing energy supply unit is connected to the primary coil. A fixing device characterized in that the temperature of the cylindrical heat generating portion is stabilized by the temperature characteristic of the value, and the electric power supplied from the fixing energy supplying portion is shut off while the image forming apparatus is in a standby state. 9. The fixing device according to claim 4, 5 or 6, wherein when the image forming apparatus equipped with the fixing device is in operation, the resistance of the positive temperature coefficient thermistor is maintained while the fixing energy supply portion is connected to the primary coil. The temperature of the cylindrical heat generating portion is stabilized by the temperature characteristic of the value, and when the image forming apparatus is on standby, the temperature of the cylindrical heat generating portion is set to be higher than the fixing temperature based on the output of the detector that detects the temperature of the fixing roller. A fixing device characterized by being stabilized at a low predetermined temperature.